<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        *{
            margin:0;
            padding:0;
        }
        div{
            height:200px;
            width:200px;
            background-color: aqua;
            /* 水平居中和垂直居中 */
            position: absolute;
            left:50%;
            top:50%;
            /* margin-left:-50px; */
            transform: translate(-50%,-50%);
        }
      
    </style>
</head>
<body>
    <div></div>
</body>
</html>